1. Field of the Invention
The present invention relates to a thermally actuated micro mirror in which a mirror surface can be tilted by causing a support structure section to generate heat by the application of electricity, and to an electronic device having the thermally actuated micro mirror.
2. Description of the Related Art
Thermally actuated micro mirrors are used in optical systems of, for example, optical scanners and printers. In the thermally actuated micro mirrors, a mirror surface is tilted by causing a support structure section to generate heat by the application of electricity, and, for example, laser light is thereby deflected and scanned on a target.
FIGS. 15A and 15B show a known type of thermally actuated micro mirror.
A thermally actuated micro mirror 1000 shown in FIGS. 15A and 15B includes a rectangular mirror surface 1001 and a fixed section 1003. Electrodes 1004 are formed on the fixed section 1003, and the mirror surface 1001 is supported relative to the fixed section 1003 by a thermally actuated support structure section 1005 in a so-called cantilevered manner.
The support structure section 1005 is deflected like a bimetal by applying electricity thereto through the electrodes 1004, as shown in FIG. 16, thereby turning the mirror surface 1001 on a turning axis 1006 to tilt at an arbitrary angle θ. In a state in which the mirror surface 1001 is turned by the angle θ, the turning axis 1006 is placed inside the support arm 1005 and outside the mirror surface 1001. In actuality, the turning axis 1006 is not fixed, but moves along the support arm 1005 as the angle θ of the mirror surface 1001 increases because the support structure section 1005 does not deflect in the shape of an ideal arc.
In such a known thermally actuated micro mirror 1000, when laser light L applied onto the mirror surface 1001 is deflected, as shown in FIG. 17A, the following problem arises. As the angle θ of the mirror surface 1001 changes, not only the incident angle of the laser light L, but also a reflecting position 1007 for the laser light L moves on the mirror surface 1001.
In this case, the reflecting position 1007 for the laser light L considerably moves, and this sometimes hinders the design of the optical system. The reflecting position 1007 thus moves with the change of the angle θ of the mirror surface 1001 because the turning axis 1006 of the mirror surface 1001 moves with the change of the angle θ, as described above.
FIG. 17B shows a case in which a turning axis 1010 of a mirror surface 1012 coincides with a reflecting position 1014 for laser light L. In this case, the reflecting position 1014 does not move on the mirror surface 1012.
FIG. 18 shows another known thermally actuated micro mirror 1020. A mirror surface 1024 of the thermally actuated micro mirror 1020 is supported perpendicularly to a fixed section 1026 by a support structure section 1030 and a support structure section 1040. The support structure section 1030 and the support structure section 1040 are deflected by applying electricity thereto. The support structure section 1030 is deflected to turn the mirror surface 1024 in a first axial direction, and the support structure section 1040 is deflected to turn the mirror surface 1024 in a second axial direction. While the thermally actuated micro mirror 1020 is a so-called two-dimensional mirror, the reflecting position for the laser light on the mirror surface greatly moves, the design of the optical system is difficult, and the area of the mirror surface 1024 must be large.
In the known thermally actuated micro mirror 1000 shown in FIGS. 15A and 15B, the area of the mirror surface 1001 must also be large. This is because the turning axis 1006 moves and the reflecting position 1007 for the laser light L moves on the mirror surface 1001 as the angle θ of the mirror surface 1001 increases, as described above. Such an increase in size of the mirror surface 1001 is significantly disadvantageous in terms of size to a mirror for use in, for example, an MEMS (Micro-Electro-Mechanical System).
The known thermally actuated micro mirrors also have the following problems:
Since the mirror surface is tilted by applying electricity to the support structure section, when the temperature of the support structure section itself changes with a change in ambient temperature, the support structure section is thereby deflected.
Portable telephones are sometimes used in various working environments, for example, at a temperature of less than −10° C. outdoors in cold districts, and at approximately 50° C. in the car parked in the summer. That is, the thermally actuated micro mirror like a bimetal is unnecessarily tilted by such a temperature difference of 60° C. This reveals that the initial angle of the mirror surface of the micro mirror depends on the temperature, such as ambient temperature, and that the micro mirror is significantly difficult to use.
The following mirrors have been proposed hitherto.
Japanese Unexamined Patent Application Publication No. 2001-249300 discloses a mirror that turns on its turning axis, and that has recesses for reinforcement. Japanese Unexamined Patent Application Publication No. 2001-264672 discloses a structure in which a mirror turns on a beam serving as a turning axis, and ribs for reinforcing the mirror extend perpendicularly to the beam as the turning axis.
Japanese Unexamined Patent Application Publication No. Hei 6-180428 teaches that a two-axis gimbal mirror that is driven by electrostatic force. The mirror turns on twistable beams serving as turning centers. Japanese Unexamined Patent Application Publication No. 8-262364 discloses a mirror that is mounted in a cantilevered manner at the leading ends of beams made of a shape-memory alloy, and that is tilted by deflecting the beams. When driving is performed by electrostatic force, the voltage must be high, and in general, it is difficult to achieve a large tilting angle. For that purpose, driving is frequency performed by resonance.
When resonance is used, it is difficult to control the angle and to perform tilting in a biased manner in which the time-phase relationship is not sinusoidal. Since the above mirror using a shape-memory alloy is mounted in a cantilevered manner, the center axis is displaced.